Segmental mediolytic arteritis: a clinical pathologic study.

A distinct arterial lesion was observed in the large abdominal muscular arteries in three autopsied patients. The salient histopathologic feature of this arterial lesion was either partial or total mediolysis. This was accompanied by a linear fibrin deposit between the media and adventitia and a variable nonpleomorphic inflammatory infiltrate. Total mediolysis led to the formation of arterial gaps. Disecting aneurysms frequently occurred and began either adjacent to arterial gaps or as a result of capillary hemorrhages in areas of partial mediolysis. Ruptured aneurysms led to massive intraabdominal hemorrhages. Arterial luminal occlusion, either by thrombi or dissection, resulted in ischemic bowel changes and renal infarcts. In addition, the arteries affected by mediolysis also showed medial degenerative changes, akin to cystic medial necrosis. Concomitant changes in the kidney showed mesangial hyperplasia; the heart exhibited histiocytic infiltrates and rare Aschoff-like bodies and capsular inflammation were seen in the spleen. The pathogenesis of the arterial lesions is unknown. A possible explanation is that this arteritis may have been induced by immune complexes and that local arterial medial degenerative changes predispose the involved arteries to immunologic injury.